Disc recorder/reproducer

ABSTRACT

The present invention provides a disk recording-playback device comprising a laser drive circuit  15  for feeding a drive signal to an optical head  4  and adjusting the power of a laser beam irradiated by the optical head  4 , an error correcting circuit  11  for detecting an error rate of a reproduced signal, and a system controller  10  for controlling operation of the laser drive circuit for signal reproduction and signal recording based on the output of the error correcting circuit  11 . The system controller  10  successively sets the laser powers to at least three different values, obtains evaluation data for each laser power, approximates the relationships between the laser powers and the evaluation data to a quadratic curve, whereby an optimum laser power is derived corresponding to a vertex of the quadratic curve. Accordingly the optimum reproduction power and recording power are set, to thereby record and reproduce signals with high accuracy.

TECHNICAL FIELD

[0001] The present invention relates to disk recording-playback devicesfor recording signals on disks or reproducing signals-from the disks byirradiating the disk with a laser beam from an optical head.

BACKGROUND ART

[0002] For use as recording media in such disk recording-playbackdevices, magneto-optical disks have been developed which permitrewriting and have a great memory capacity and high reliability. Suchdisks have found wide use as external memories in computers and audiovisual devices. Developed especially in recent years are techniques forachieving improved recording densities by forming lands 17 and grooves18 alternately on the signal bearing surface of a magneto-optical disk 1as shown in FIG. 20 and recording signals on both the land 17 and thegroove 18.

[0003] The lands 17 and the grooves 18 are wobbled as illustrated, andthe wobbling frequency is a predetermined center frequency asfrequency-modulated. A wobble signal is detected by signal reproduction,and the rotation of the magneto-optical disk is so adjusted that thewobble signal has the center frequency at all times, whereby constantlinear velocity control is realized. Various items of information(wobble information) such as address information are contained in thewobble signal which is frequency-modulated as stated above. Variouscontrol operations are realized based on the wobble information at thetime of signal reproduction.

[0004] With the disk recording-playback device of a laser-pulsedmagnetic field modulation type, a laser beam is projected onto the diskfor signal reproduction, and a laser beam is also projected onto thedisk for signal recording, and the disk is heated locally. Furthermore,with magneto-optical disks using magnetic super resolution, signalreading is started whereupon the temperature in a beam spot regionreaches a predetermined value while laser power for signal reproductionis increased. The laser power for signal reproduction is set lower thanthe laser power for signal recording, so that there is no likelihoodthat the recorded signals are damaged along with signal reproduction.

[0005] With the disk recording-playback device, power (recording power)of the laser beam for signal recording and power (reproduction power) ofthe laser beam for signal reproduction have optimum values,respectively. If a power differs from the optimum value, a bit errorrate of the reproduced signal increases. If the bit error rate exceeds agiven specified value, difficulty is encountered in performing a normalreproduction operation (see FIG. 14). Accordingly, already proposed is amethod for, in the system's initiation into operation, reproducingsignals and calculating the error rate while the reproduction power isgradually altered, or recording signals and calculating the error rateof the reproduction signal while the recording power is graduallyaltered for test tracks pre-provided on the disk, and thereby retrievingan optimum reproduction power and a recording power having the lowesterror rate.

[0006] However, with the disk recording-playback device, the step widthin the alteration of the reproduction power and the recording power isrequired to be set as small as possible in order to retrieve the optimumreproduction power and the optimum recording power with high accuracy,with the result that a long period of time is required for theretrieval, entailing the problem that the device's initiation intooperation takes much time.

[0007] An object of the present invention is to provide a diskrecording-playback device which is capable of jumping to signalrecording or to signal reproduction in a short period of time andrecording and reproducing signals with high accuracy at all times bysetting the optimum reproduction power and recording power for eachdisk.

DISCLOSURE OF THE INVENTION

[0008] The present invention provides a disk recording-playback devicewhich comprises a laser drive circuit for feeding a drive signal to anoptical head and adjusting the power of a laser beam irradiated by theoptical head, an evaluation data detecting circuit for detectingevaluation data representing quality of a signal reproduction state, acontrol circuit for controlling operation of the laser drive circuitbased on an output of the evaluation data detecting circuit. The controlcircuit comprises:

[0009] calculation processing means for setting the laser powers to atleast three different values successively, obtaining evaluation data foreach laser power and approximating the relationships between the laserpowers and the evaluation data at the three points to a quadratic curve,and thereby deriving an optimum laser power corresponding to a vertex ofthe quadratic curve,

[0010] laser power control means for preparing a laser power controlsignal so as to make the optimum laser power a target value and feedingthe signal to the laser drive circuit. Usable as the evaluation data is,for example, the frequency of occurrence of a bit error included in thereproduced signal, i.e. error rate.

[0011] In recording or reproducing a signal to a disk, the diskrecording-playback device of the present invention, at first, determinesthe optimum laser power for the disk. For example, test trackspre-provided on the disk are used in determining the optimum laser powerfor signal recording. The signals are recorded to the test tracks withdifferent laser powers, and thereafter signal reproduction is performedwith an appropriate laser power, to detect the error rate of thereproduced signal. Thus the relationship between the laser power(recording power) and the error rate at each of the three points P1, P2and P3 is plotted, as shown in FIG. 16.

[0012] The relationships between the recording powers and the errorrates can be approximately illustrated by a quadratic curve. When thecoordinates of at least three points are decided, the quadratic curve isuniquely determined. The quadratic curve can be decided by using thevalues of laser power and error rate at the three points P1, P2 and P3,as stated above. The laser power corresponding to the vertex of thequadratic curve is the optimum laser power Pwo for minimizing the errorrate, as shown in FIG. 16. The control circuit prepares, for signalrecording, a laser power control signal so as to make the optimum laserpower Pwo a target value to feed the signal to the laser drive circuit.As a result, signal recording is performed with the optimum laser power,obtaining a reproduced signal having an error rate sufficiently lowerthan a prescribed value for the subsequent signal reproduction.

[0013] All the error rates of the three points for determining thequadratic curve are not required to be lower than the prescribed value.A given value can be set as a laser power, so that the conventionalretrieving processing is not completely necessary.

[0014] Stated specifically the control circuit optimizes the laser powerfor signal reproduction, and thereafter optimizes the laser power forsignal recording by the calculation processing means and the laser powercontrol means. In this case, in order to optimize the laser power forthe signal reproduction, the control circuit comprises retrieving meansfor retrieving a lower limit value having a smaller value from two limitvalues of the laser power wherein evaluation data is beyond apredetermined allowable value, and means for determining the optimumlaser power based on the lower limit value retrieved. The means fordetermining the optimum laser power determines the optimum laser powerby adding a predetermined value to the lower limit value retrieved or bymultiplying the retrieved lower limit value by a predetermined value.

[0015] According to the specific construction stated above, the laserpower for reproduction is optimized based on the principle which will bedescribed below. In signal reproduction, the variations in reproductionpower alter the error rates of the reproduced signals in a quadraticcurve, for example, as shown in FIG. 15. On a characteristics curveillustrated in a solid line, the optimum reproduction power Pr whereinthe error rate is minimum value is present, for example. The laser powerfor signal reproduction is required to be set between the two limitvalues wherein the error rate is smaller than a prescribed value, i.e.between the lower limit reproduction power Prmin and the upper limitreproduction power Prmax. Similarly in signal recording, the optimumrecording power Pw wherein the error rate is minimum is present. Thelaser power for signal recording is required to be set between the twolimit values wherein the error rate of the reproduction signal issmaller than a prescribed value, i.e. between the lower limit recordingpower Pwmin and the upper limit recording power Pwmax.

[0016]FIG. 17 shows the range of the reproduction power Pr and therecording power Pw wherein the error rates are smaller than theprescribed values, respectively. It is thought that there will be notrouble in signal reproduction and recording if the reproduction powerPr and the recording power Pw are each set to a given value within thisrange. The reproduction power and the recording power are, however,preferably set at central possible positions within the range since thecharacteristics shown in FIG. 17 vary due to disk warp and the like.Usable as a method for optimizing the reproduction power, for example,is to calculate the average value of the lower limit reproduction powerPrmin and the upper limit reproduction power Prmax wherein the errorrates are smaller than the prescribed value, respectively, and todetermine the calculated result as the optimum reproduction power.

[0017] However, the reproduction power Pr wherein the error rate issmaller than the prescribed value is dependent on the recording power Pwwherein the error rate is smaller than the prescribed value, asdescribed in FIG. 17. While the recording power Pw is in the range of6.5 mW to 8.0 mW, for example, a limit reproduction power Pr wherein theerror rate is smaller than the prescribed value varies in accordancewith the recording power. Accordingly in the case where, within therange of this recording power, the optimum reproduction power isdetermined as the average value of the lower limit reproduction powerPrmin and the upper limit reproduction power Prmax wherein the errorrates are smaller than the prescribed values, respectively, the value ofthe optimum reproduction power deviates from the center position of therange shown in FIG. 17. Since the variations in the characteristicsshown in FIG. 17 greatly shift the reproduction power from the optimumvalue, it is likely that the error rate is beyond the prescribed value.

[0018] According to the specific construction described, in order to setthe reproduction power and the recording power to values provided atpossible central positions within the range shown in FIG. 17, when thereproduction power is optimized, the optimum reproduction power iscalculated by firstly retrieving the lower limit reproduction powerPrmin wherein the error rate is smaller than the prescribed value andthereafter adding a predetermined value to the retrieved lower limitreproduction power Prmin. Usable as the predetermined value are thevalues within the area wherein the reproduction power is not dependenton the recording power in the relationship shown in FIG. 17, i.e., 0.36mW: one half of the difference between the maximum reproduction power2.56 mW and the minimum reproduction power 1.84 mW wherein the recordingpower is greater than 8.0 mW or values close to 0.36 mW (for example,0.4 mW). Consequently obtained for the reproduction power is the optimumvalue which is not dependent on the recording power.

[0019] As shown in FIG. 15, even if the optimum value for thereproduction power changes from Pr to Pr′ or to Pr″ since the variationcharacteristics of the error rate relative to the reproduction powervary from a solid line to a broken line or to a chain line, the lowerlimit reproduction power Prmin changes to Prmin′ or to Prmin″, and thedifference between the optimum value Pr, Pr′ or Pr″, and the lower limitreproduction power Prmin, Prmin′ or Prmin″, respectively, is anapproximately constant value N. Accordingly, the accurate optimumreproduction power Pr, Pr′ or Pr″ can be determined by adding thedifference N to the lower limit reproduction power Prmin, Prmin′ orPrmin″, respectively. Furthermore, the accurate optimum reproductionpower Pr, Pr′ and Pr″ can also be determined by multiplying the lowerlimit reproduction power Prmin by a predetermined value α instead ofadding the predetermined value N to the lower limit reproduction powerPrmin.

[0020] As described above, the disk recording-playback device of thepresent invention can jump to signal recording or to signal reproductionin a short period of time, and record and reproduce signals with highaccuracy at all times by setting the optimum reproduction power andrecording power for each disk.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a block diagram showing the construction of a diskrecording-playback device embodying the present invention.

[0022]FIG. 2 is a flow chart showing a laser power control procedure foruse in the device.

[0023]FIG. 3 is a flow chart of test read/write and an update routinefor a management table.

[0024]FIG. 4 is a flow chart showing a control procedure of arecording-playback operation for a normal operation.

[0025]FIG. 5 includes a diagram for illustrating data structure of themanagement table.

[0026]FIG. 6 is a diagram illustrating an example of the updatedmanagement table.

[0027]FIG. 7 is a graph showing the relationship between temperature andlaser power of the management table when the device is initiated intooperation.

[0028]FIG. 8 is a graph showing the relationship between temperature andlaser power of the management table in the first test read/write.

[0029]FIG. 9 is a graph showing the relationship between temperature andlaser power of the management table in the second test read/write.

[0030]FIG. 10 is a flow chart showing a procedure for reproduction poweroptimization.

[0031]FIG. 11 is a flow chart showing a procedure for recording poweroptimization.

[0032]FIG. 12 is a flow chart showing another procedure for recordingpower optimization.

[0033]FIG. 13 is a graph showing a process for reproduction poweroptimization.

[0034]FIG. 14 is a graph showing the relationship between thereproduction power and the error rate.

[0035]FIG. 15 is a graph illustrating the principle of the reproductionpower optimization.

[0036]FIG. 16 is a graph illustrating the principle of the recordingpower optimization.

[0037]FIG. 17 is a diagram showing the relationship between therecording power and the reproduction power each of which satisfies aprescribed value.

[0038]FIG. 18 is a waveform diagram of the two reference signals writtenin a header of the reproduced signal.

[0039]FIG. 19 is a graph showing the relationship between amplituderatio of the reproduced signals of the two reference signals and thereproduced power.

[0040]FIG. 20 is an enlarged perspective view of lands and groovesformed on a magneto-optical disk.

BEST MODE OF CARRYING OUT THE INVENTION

[0041] With reference to the drawings, a detailed description will begiven below of the present invention as embodied into diskrecording-playback devices for use with magneto-optical disks serving asrecording media. FIG. 1 shows a disk recording-playback device embodyingthe invention and comprising a spindle motor 2 for rotatingly driving amagneto-optical disk 1. A temperature sensor 16 is provided in thevicinity of the magneto-optical disk 1.

[0042] The device has a signal reproduction system comprising a laserdrive circuit 15, optical head 4, reproduced signal amplifying circuit5, reproduced signal detecting circuit 7 and error correcting circuit11. For signal reproduction, the optical head 4 is driven by the laserdrive circuit 15 to irradiate the disk 1 with a laser beam. On the otherhand, the device has a signal recording system comprising a magnetichead drive circuit 14 and a magnetic head 3. For signal recording, thelaser drive circuit 15 and the optical head 4 operate for heating thedisk 1 locally. The device further has a control system comprising aservo circuit 6, external synchronizing signal producing circuit 8,system controller 10, memory 9, delay circuit 12 and timing pulsegenerating circuit 13.

[0043] The optical head 4 projects a laser beam onto the disk 1, anddetects the reflected beam as an optical signal and a magneto-opticalsignal. The amplifying circuit 5 amplifies the optical signal andmagneto-optical signal obtained by the optical head 4 and then feeds afocus error signal and a tracking error signal contained in the opticalsignal to the servo circuit 6. The amplifying circuit 5 also feeds anoptical signal, which is detected due to discrete regions provided at aconstant interval in the grooves of the disk 1, to the externalsynchronizing signal producing circuit 8 and the magneto-optical signalto the reproduced signal detecting circuit 7.

[0044] The circuit 8 produces an external synchronizing signal and feedsthe signal to the servo circuit 6 and the delay circuit 12. In responseto the focus error signal and tracking error signal, the servo circuit 6executes focusing servo and tracking servo for an actuator (not shown)provided for the optical head 4, and also controls the rotation of thespindle motor 2 based on the external synchronizing signal.

[0045] The reproduced signal detecting circuit 7 feeds the detectedreproduced signal to the error correcting circuit 11. The circuit 11demodulates the reproduced signal, detects errors from the reproducedsignal thus obtained, corrects the errors, and outputs the reproduceddata as corrected to the subsequent circuit. The delay circuit 12prepares a synchronizing signal by delaying the phase of the externalsynchronizing signal by a predetermined time period and feeds the signalto the timing pulse generating circuit 13.

[0046] For signal recording, the timing pulse generating circuit 13receives the data to be recorded and modulated by a specified method andthe synchronizing signal from the delay circuit 12, prepares a pulsesignal for applying an alternating magnetic field to the disk 1, feedsthe signal to the magnetic head drive circuit 14, also prepares a pulsesignal (write clock) for irradiating the disk 1 with a pulse beam andfeeds the signal to the laser drive circuit 15. For signal reproduction,the reproduced signal detecting circuit 7 converts a reproduced analoguesignal to a digital signal based on the synchronizing signal (readclock) from the delaying circuit 12.

[0047] The magnetic head drive circuit 14 prepares a drive signal forthe magnetic head 3 based on the pulse signal from the timing pulsegenerating circuit 13. The magnetic head 3 applies an alternatingmagnetic field to the disk 1 based on the drive signal from the headdrive circuit 14. The laser drive circuit 15 drives a semiconductorlaser (not shown) provided on the optical head 4 based on the pulsesignal from the timing pulse generating circuit 13. The optical head 4produces a laser beam based on the drive signal from the laser drivecircuit 15 and irradiates the disk 1 with the beam.

[0048] Based on the external synchronizing signal obtained from thesignal producing circuit 8, the system controller 10 controls theoperation of the delay circuit 12. Further the system controller 10calculates the bit error rates based on the error correction informationobtained from the error correcting circuit 11, and controls theoperation of the laser drive circuit 15 in response to the result of thecalculation. Furthermore, the system controller 10 accumulates in amanagement table of the memory 9 temperature data obtained from thetemperature sensor 16 and the optimum read power and the optimum writepower determined in test read and test write which will be describedbelow, and controls the laser power by reference to the management tablefor signal reproduction and signal recording.

[0049] The laser drive circuit 15 adjusts the power of the laser beamirradiated from the optical head 4 for signal reproduction in responseto a laser power control signal Cp to be fed from the system controller10, as will be described below. As shown in FIG. 5, stored in themanagement table are, for each temperature, read power Pr, write powerPw, flag Test RW indicating whether test read/write has been executed,flag indicating whether the interpolation processing as will bedescribed below has been performed, flag indicating whether atemperature concerned has actually been experienced.

[0050]FIG. 2 shows the overall flow of a procedure to be executed by thesystem controller 10. First in step S1 a new magneto-optical disk isinserted. In step S2 an old management table is cleared, and thereaftera reference table wherein a reference value (initial value) of therelationship between temperature and laser power (Pr or Pw) isprescribed is prepared. Subsequently in step S3 an initial temperatureT_initial is detected. In step S4 the laser power when the device isinitiated into operation is determined according to a predeterminedreference temperature Tdef, reference laser powers Pwdef and Prdef, andinitial temperature T_initial.

[0051] Subsequently in step S5 the initial temperature T_initial is setto current temperature T and interior temperature held by the system.Then step S6 follows to execute the test read/write and update routinefor the management table. In executing the test read/write and theupdate routine for the management table, the test read and test writeare performed (Test RW) with use of predetermined test tracks, tocalculate optimum laser powers Pr, Pw in step S21 as described in FIG.3. In step S23 the laser powers Pr, Pw at temperature T prescribed inthe management table are updated based on the calculation result.

[0052] Next step S24 follows to give a checking mark to a Test Rw termas for a temperature wherein the laser power is optimized. Then step S25follows to derive, by interpolation processing, optimum laser powers Pr,Pw as for each of the temperatures between the two temperatures whereinchecking marks are given to the Test Rw terms with use of the data onthe two temperatures. Step S26 follows to give checking marks to theinterpolation terms as for the temperatures given interpolationprocessing to complete the procedure for updating the management table.

[0053] As shown in FIG. 6, in the case where, for example, therelationship between a disk temperature and an initial temperature oflaser power, i.e. slope (hereinafter referred to as temperature slope)of variations of laser power relative to disk temperature, is specified,when the temperature for operation initiation is 25° C., and the optimumlaser power is “62” calculated after the test read/write, the initialvalue “64” is updated to “62”. Subsequently, in the interpolationprocessing, the laser power at 25° C. is set to a base point, and thesame value “2” is subtracted from each of the laser powers as for theother temperatures, whereby the interpolation is processed with thetemperature slope held to update the management table. FIG. 7 shows anexample wherein the relationship between the disk temperature and theinitial value of the laser power is updated at 25° C. by the testread/write. Accordingly, the management table is updated as thetemperature slope is held constantly.

[0054] Thereafter for normal reproduction, first in step S7 shown inFIG. 2 a disk temperature T is detected. In step S8 an inquiry is madeas to whether the disk temperature is increased by 5° C. or more. Whenthe answer is affirmative, step S9 follows to update a systemtemperature T_sys to the temperature T. Next in step S10 an inquiry ismade as to whether the temperature has been already experienced in themanagement table. If the answer is negative, step S11 follows to executetest read/write and the management table updating routine as shown inFIG. 3.

[0055] To take an example shown in FIG. 6, in the case where the testread/write is performed at 30° C. for the first time, when the optimumlaser power determined by the test read/write is “59”, the laser power“57” is updated to “59”, laser powers as for the temperatures between25° C. and 30° C. are determined by the interpolation processing (linearinterpolation), in the temperature range of less than 25° C. and ofgreater than 30° C., the interpolation is processed so as to hold thetemperature slope constant, and the management table is updated. FIG. 8shows the state wherein the management table is updated by the abovetest read/write.

[0056] Furthermore, as shown in FIG. 6, in the case where the testread/write is performed at 35° C. for the second time, when the optimumlaser power determined by the test read/write is “50”, the laser power“54” is updated to “50”, laser powers as for the temperatures between30° C. and 35° C. are determined by the interpolation processing (linearinterpolation), in the temperature range of greater than 35° C. theinterpolation is processed so as to hold the temperature slope constant,and the management table is updated. FIG. 9 shows the state wherein themanagement table is updated by the above test read/write.

[0057] Accordingly whenever the temperature varies by 5° C. or more, thetest read/write is executed, to determine the optimum laser power as forthe temperature at that time, executing the interpolation processingwith use of the data, to thereby update the management table. When allthe experienced terms of the management table are given checking marks,the read power Pr and the write power Pw are set for the subsequentnormal operation, by referring to the relationship between thetemperature and the laser power stored in the management table, and thesignals are recorded and reproduced.

[0058] Thus, for normal operation, in step S31 the disk temperature isdetected, followed by step S32 wherein an inquiry is made as to whethera recording-playback request is made, as shown in FIG. 4. When theanswer for step S32 is affirmative, step S33 follows to refer to themanagement table. In step S34 the laser powers Pr, Pw are set inaccordance with the temperature concerned. In step S35recording-playback operation is executed, to complete the procedure.

[0059] Next, a method for optimizing the reproduction power will bedescribed as follows. The present example adopts a procedure shown inFIGS. 13 and 14 for retrieving a lower limit value Prmin having asmaller value from the two limit values of reproduction power whereinthe error rate is smaller than the prescribed value in the test read forthe determination of the optimum reproduction power. That is the threestates shown in FIG. 13 are assumed, depending on the initial values ofthe reproduction power. When the reproduction power is smaller than thelower limit value as in the case of A, the reproduction power isincreased. When the reproduction power is between the lower limit valueand the upper limit value as in the case of B, the reproduction power isdecreased. When the reproduction power is greater than the upper limitvalue as in the case of C, the reproduction power is decreased. Thus thereproduction power is altered to the lower limit value Prmin shown inFIG. 14 or values close to the lower limit value. Thereafter apredetermined value N is added to the reproduction power concerned, tothereby determine the optimum reproduction power Pr.

[0060] In order to distinguish the case A from the case C shown in FIG.13, the present example adopts a procedure using a following principle.The signal recorded on the magneto-optical disk has data format whereina plurality of frames are arranged in time-series. Each of the frames isprovided with a header portion wherein a first reference signal of asingle frequency having a short cycle (2T) and a second reference signalof a single frequency having a long cycle (8T) are recorded, as shown inFIG. 18. With reference to FIG. 19, the ratio (W2/W1) of amplitude W2 ofthe reproduced signal of the second reference signal to amplitude W1 ofthe reproduced signal of the first reference signal is increased as thereproduction power Pr rises. Consequently, when the ratio is smallerthan a predetermined set value, the state is judged as A in FIG. 13.When the ratio is greater than a predetermined set value, the state isjudged as C in FIG. 13.

[0061]FIG. 10 shows a specific procedure for optimizing the reproductionpower by the test read for the grooves of the test tracks precedentlyprovided on the magneto-optical disk. First in step S42 shown in FIG. 10an initial value is set as write power Pw. In step S43 recording isperformed to the test tracks. Next in step S44 an initial value is setas reproduction power Pr. In step S45 the test tracks are reproduced, itis decided whether the reproduction is allowable depending on whetherthe error rate concerned is greater than a threshold value. When thereproduction is allowable, the current state is shown as FIG. 13 B,followed by step S46 wherein the reproduction power Pr is decreased by aunit power (“1”). Then in step S47 the test tracks are reproduced onceagain, and an inquiry is made as to whether the reproduction isallowable. Thereafter the sequence returns to step S46 to repeat thesame procedure.

[0062] When the answer for step S47 is negative, the sequence proceedsto step S48 wherein the lower limit value Pr1 is determined by adding aunit power (“1”) to the reproduction power Pr. In step S49 the optimumreproduction power Pr_opt is determined by adding a predetermined valueN (=0.4 mW) to the lower limit reproduction power Pr1, to complete theprocedure. In determining the optimum reproduction power Pr_opt, usableis a method wherein the lower limit reproduction power Pr1 is multipliedby a predetermined value α. The predetermined value α can be set as avalue dependent on the system.

[0063] On the other hand, when the reproduction is not allowable in stepS45, the state concerned is shown as FIG. 13 A or C. Based on theprinciple described in FIGS. 18 and 19, it is judged which of FIG. 13 Aor C shows the state concerned, i.e., in step S50 shown in FIG. 10 aninquiry is made whether the ratio (W2/W1) of the reference signals isgreater than a set value A, to thereby recognize a direction to whichthe reproduction power will be changed. Instead of usage of the ratio(W2/W1) of reference signal, it is possible to recognize a direction towhich the reproduction power will be changed depending on whether thedifference (W2−W1) between the reference signals is greater than a setvalue.

[0064] When the answer for step S50 is affirmative, the state concernedis shown in FIG. 13 C, followed by step S51 wherein the reproductionpower Pr is decreased by a predetermined value n. In step S52 an inquiryis made as to whether the reproduction power Pr is greater than a setlower limit value Pr_min. If the answer is affirmative, step S53 followsto reproduce the test tracks to judge whether the reproduction isallowable. When it is judged that the reproduction is not allowable instep S53, the sequence returns to step S51 to repeat the processingwherein the reproduction power Pr is decreased by the predeterminedvalue n. When the reproduction is allowable in step S53, the state ischanged to as in FIG. 13 B, followed by step S46 wherein the optimumreproduction power Pr_opt is determined according to the above proceduredescribed, thereby completing the procedure.

[0065] When the answer for step S50 is negative, the state concerned isshown in FIG. 13 A, followed by step S57 wherein the reproduction powerPr is increased by a single unit power (“1”). In step S58 an inquiry ismade as to whether the reproduction power Pr is smaller than a set upperlimit value Pr_max. If the answer is affirmative, step S59 follows toreproduce the test tracks to judge whether the reproduction isallowable. When it is judged that the reproduction is not allowable instep S59, the sequence returns to step S57 to repeat the processing forincreasing the reproduction power Pr. When the reproduction is allowablein step S59, step S60 follows to determine the reproduction power Pr atthat time as a lower limit value Pr1, followed by step S49 wherein theoptimum reproduction power Pr_opt is determined by adding apredetermined value N (=0.4 mW) to the lower limit reproduction powerPr1, to thereby complete the procedure.

[0066] When the answer for step S52 or S58 is negative, step S54 followsto increase the recording power Pw by a predetermined value n. Then stepS55 follows to inquire whether the recording power Pw is smaller than aset upper limit value Pw_max. If the answer is affirmative, step S43follows to write the test tracks. If the answer is negative, step S56follows to produce a warning notice “NG” and register the test tack as“NG”. With test read for lands of the test track, the optimumreproduction power Pr_opt can be determined according to the sameprocedure.

[0067] Furthermore, in determining the optimum recording power, usableis the same method as that for the reproduction power optimization asdescribed above. FIG. 11 shows a specific procedure for the recordingpower optimization according to the method. When the test read iscompleted, an initial value of recording power which value is notoptimum but recordable and the optimum reproduction power aredetermined, the recording power Pw is set to the initial value in stepS63. In step S64 the recording and reproduction are performed for thetest tracks, to judge whether the reproduction is allowable. When thereproduction is not allowable, step S65 follows to produce a warningnotice “NG” and register the test tracks as “NG”. During an operationstate the recording power is held at the initial value.

[0068] On the other hand, when the reproduction is allowable in stepS64, the recording power Pw is decreased by a single unit power (“1”).In step S67 an inquiry is made as to whether the recording power Pw isgreater than a set lower limit value Pw_min. When the answer isnegative, step S65 follows to produce a warning notice “NG” and registerthe test track as “NG”. During an operation state, the recording poweris held at the initial value. If the answer for step S67 is affirmative,the recording and reproduction are performed for the test tracks tojudge whether the reproduction is allowable in step S68. When it isjudged that the reproduction is allowable, step S69 follows to alterwrite data or to shift location to write data on. The sequence returnsto step S66 to repeat a processing for decreasing the recording power.

[0069] Thereafter when it is judged that the reproduction is notallowable in step S68, step S70 follows to determine a lower limit valuePw1 by adding a single unit power “1” to the recording power Pw at thattime. In step S71 an optimum recording power Pw_opt is determined byadding a predetermined value N to the lower limit recording power Pr1 tocomplete the procedure. In determining the optimum recording powerPw_opt, usable is a method wherein the lower limit recording power Pw1is multiplied by a predetermined value α. The predetermined value α canbe determined as a value dependent on the system.

[0070] In determining the optimum recording power, usable is a methodwherein the relationship between the recording power and the bit errorrate is approximated to a quadratic curve, as shown in FIG. 16. Forexample, signals are recorded with different laser powers for testtracks pre-provided on the disk, thereafter the signals are reproducedwith an appropriate laser power, and the error rate for the reproductionsignal is detected. As a result, the relationship between a laser power(recording power) and an error rate at each of the three points P1, P2and P3 is plotted, as shown in FIG. 16. The relationship can beapproximately illustrated by a quadratic curve. When the coordinates ofat least three points are decided, the quadratic curve is uniquelydetermined.

[0071] Accordingly, a quadratic curve illustrating the relationshipbetween the laser power and the error rate can be determined with use ofthe values of the laser power and the error rate at the three points,P1, P2 and P3. As shown in FIG. 16, the laser power corresponding to thevertex of the quadratic curve is the optimum laser power Pwo forminimizing the error rate.

[0072]FIG. 12 shows a procedure for optimizing the recording power basedon the quadratic curve approximation. When the test read is completed,and an initial value of recording power which value is not optimum butrecordable and the optimum reproduction power are determined, therecording power Pw is set to the initial value in step S83. In step S84the recording and reproduction are performed for the test tracks, tojudge whether the reproduction is allowable. When it is judged that thereproduction is not allowable, step S85 follows to produce a warningnotice “NG” and register the test tracks as “NG”. During an operationstate the recording power is held at the initial value.

[0073] On the other hand, when it is judged that the reproduction isallowable in step S84, the recording power Pw1 and the bit error rateBER concerned are stored in the memory. Next in step S87, the recordingpower Pw is decreased by a predetermined value n, followed by step S88wherein the recording and the reproduction are performed for the testtracks to judge whether the reproduction is allowable. When it is judgedthat the reproduction is allowable, step S87 returns to repeat theprocedure for decreasing the recording power. As a result when it isjudged that the reproduction is not allowable in step S88, step S89follows to store in the memory the recording power Pw2 and the bit errorrate BER which are not allowable for the reproduction.

[0074] Subsequently in step S90 the recording power Pw is increased by apredetermined value n, followed by step S91 wherein the recording andthe reproduction are performed onto the test tracks to judge whether thereproduction is allowable. When it is judged that the reproduction isallowable, step S90 returns to repeat the procedure for increasing therecording power. As a result, when it is judged the reproduction is notallowable in step S91, step S92 follows to store the recording power Pw3and the bit error rate BER which are not allowable for the reproduction.Thereafter in step S93 the relationships between the laser powers andthe bit error rates are approximated to a quadratic curve with use ofthe data of the three points (Pw1, BER1), (Pw2, BER2), (Pw3, BER3), tocalculate a recording power serving as a central axis of the curve as anoptimum value Pw_opt. In step S94 the optimum value Pw_opt is set as therecording power Pw to complete the procedure.

[0075] As described above the present invention provides a diskrecording-playback device which is adapted to determine, with the smallnumber of steps, the optimum reproduction power which is not dependenton the recording power when the test read is performed for thedetermination of the optimum reproduction power, and the optimumrecording power is uncertain. Further in a subsequent test write fordeciding the optimum recording power, with the smaller number of steps,the optimum recording power can be determined by using the optimumreproduction power determined in the test read. The device can setaccurately the optimum reproduction power and the optimum recordingpower with simple steps as a whole. Therefore the device can reproduceor record signals in a short period of time after the system'sinitiation into operation, and execute signal recording and signalreproduction with high accuracy.

1. (Cancelled)
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 4. (Cancelled)
 5. (Amended)A disk recording-playback device wherein a disk is irradiated with alaser beam from an optical head to record signals on the disk or toreproduce signals from the disk, the disk recording-playback devicecomprising a laser drive circuit for feeding a drive signal to theoptical head and adjusting the power of the laser beam irradiated by theoptical head, an evaluation data detecting circuit for detectingevaluation data representing quality of a signal reproduction state, acontrol circuit for controlling operation of the laser drive circuitbased on an output of the evaluation data detecting circuit, the controlcircuit comprising reproduction power optimizing means for optimizingthe laser power for signal reproduction, recording power optimizingmeans for optimizing the laser power for signal recording after theoptimization processing by the reproduction power optimizing means iscompleted, and laser power control means for preparing a laser powercontrol signal so as to make the optimum recording power obtained by therecording power optimizing means or the optimum reproduction powerobtained by the reproduction power optimizing means a target value andfeeding the signal to the laser drive circuit, the diskrecording-playback device being characterized in that the recordingpower optimizing means comprises: calculation processing means forsetting the laser powers to at least three different valuessuccessively, obtaining evaluation data for each laser power andapproximating the relationships between the laser powers and theevaluation data at the three points to a quadratic curve, and therebyderiving an optimum recording power corresponding to a vertex of thequadratic curve, and the reproduction power optimizing means comprises:retrieving means for retrieving a lower limit value having a smallervalue from two limit values of the laser power wherein evaluation datais beyond a predetermined allowable value, and optimum reproductionpower determining means for determining the optimum laser power byadding, to the retrieved lower limit value, the value, or values closeto, one half of the difference between a maximum reproduction power anda minimum reproduction power within the range wherein the reproductionpower is not dependent on the recording power in the relationshipbetween the laser power for signal reproduction and the laser power forsignal recording wherein each evaluation data is in the allowable range.6. A disk recording-playback device according to claim 5 wherein theevaluation data is the frequency of occurrence of a bit error includedin the reproduced signal.